Manehattan was once a prosperous city known for being full of cultural diversity. Nowadays you can clearly see the difference between the four districts. It is almost as if they can't live peacefully without being separated. Ever since the districts split the city, it has been hard for a pony to go from one to another without sticking out.
No ponies know of when or how exactly the city became so divided, but considering tourists only go to Mane District it doesn't really affect any ponies outside of the city. It is almost as if Manehattan has no sense of harmony and harmony is what keeps Equestria strong.